Low boost on stock gauge GRRR!!!!!!
 

Just spent the past few HOURS looking for an old thread about this. I found out that it may just an electrical problem with the signals that go from the sensor to the ECU then to the gauge. How would I fix this?!?!?!?!?

My car (according to the gauge) always runs in vaccum with very little boost. if I really stand on the accelerator then my boost might come up to the middle where there is no boost nor vacuum...

any ideas? or can someone point me in the right direction of the thread that has covered this?

thank you for your time and HELP,

TR

Install a real boost gauge. Then tell use what the numbers are.

Your wasting your time at this point without installing real boost gauge.

James

I have an Apexi mechanical boost gauge that is sitting in it's box on my passenger seat, waiting to be intsalled. he he... I guess this weekend would be a good time to do it.

thank you,
TR

Wankel7 is right, there are several reasons the gauge will read low, but if you don't know what the manifold pressure really is you won't be able to figure out which one it is.

If the Apexi gauge shows boost actually is low, look for plumbing leaks and check the condition of the turbo. If it shows boost is okay, either the gauge or the MAP sensor is faulty. Check the MAP sensor voltage at the ECU and compare it to the numbers in the FSM. If the reading is low then you should replace the sensor. If it's okay then it's probably just a bad gauge, which doesn't matter because you have a new one.

Ok, after installing the Apexi gauge yesterday I started the car and the NEW "real" gauge shows at idle -500mm Hg, in neutral revving the engine to about 5,000rpm the Apexi gauge will only show up to about -100mm Hg. driving the car will get the boost to about 0.5 BAR in third gear. I'll be checking for vacuum leaks and leaks in the intake system today along with removing the TID and checking to make sure that the turbo does not have excessive (any) friction in the shaft.

any reccommendations as to where i might look?

only thing i can think of is that when i got my injectors back from being ultrasonically cleaned the slid into the block pretty easily, maybe there is a leak there.

thank you for all your help,
Ryosuke

EDIT: I will post a vid of the gauge and RPM if needed or wanted.

What are the mods to the car?

.5 bar = 7.25 psi

Depending on your mods.....that could be normal boost.

The best way to check for intake leaks is this....go to home depot into the plumbing section and buy one of those rubber end caps with the big hose clamp on it. Big enough to snugg around your TID. Then punch a hole in the end cap. Now stick a air hose in there and pressurize your intake system. 30 psi works well. You will hear the leaks if you have them.

thanks Wankel7, I'll stop there today while I'm out. I would think though that the boost gauge would be Zero or slightly under during idle, but then boost up at RPM.

TR

EDIT: there are no mods except the Apexi boost gauge, Apexi SAFC II, and a K&N air filter...

Considering your mods then the boost is normal...but even a lil more than stock which is like 5.5 psi I think.

Now, your gauge showes -500mm of hg at idle? That converts to about 19" of hg. That is really high vacuum for idle....what is your idle rpm at?

James

James, the idle is at about 800 +/- 25rpm. every once in a while, anout once every 7-10seconds i get a "pop" out of the exhaust. I'll go take a video and get it uploaded to a site. anyone recommend a site that will host my vid?

thank you again,
Ryosuke

-500mmHg at 800rpm would indicate a nice, healthy engine. Manifold pressure at idle is always well under atmospheric because the engine is sucking against a closed throttle.

well that sounds all well and good NZConvertable, but now i wonder why the car won't boost very well... maybe the turbo shaft is rusted. the car did sit in a barn for a number of years. I was told 2 years but it looks like the car was sitting for longer than that.

now I have to wait until next weekend before i can touch the car again. i work away from my garage so I can only get there on my days off.

thank you again for all your help,
TR

You said above you had no airflow mods except a K&N filter. Stock max boost is 0.45bar so 0.5bar sounds fine to me. I dunno what you're worried about. ;)

mainly the sputtering-pop i get out of the exhaust once in a while 7-10 second interval not really steady.

TR

EDIT: and the occasional shake at idle

EDIT2: to me the car just doesn't idle nicely like i know a rotary can idle like. i would think that it would just purr with no reciprocating objects, it would just create a "whur" under the hood. am I wrong about that one?

thanks again TR

Sounds like a very small pre-TB vac leak somewhere, which it to be expected on an unmolested 18yo engine. As long as it drives okay I really wouldn't worry about it.

Ok here is a short video of the boost charactoristics in neutral. is this normal for an FC? http://media.putfile.com/FC-Boost-charactoristics

Ryosuke

EDIT: still picyures are in my next post

here are two pictures in neutral (cant film when driving, not safe) the first is at idle, and the second is just under 5.5krpm. is it natural for there to be little to no boost at idle? and about the popping sound i get every 7-10 seconds out the exhaust would this be cause be a vac leak like NZ said or could it be due to the fact that i cannot tell where my timing is due to rust and lack of markings on the lowest belt wheel (can't recall the name off hand right now)

thank you

Honestly, just drive the car it seems just fine:)

Its old...its gonna have problems. As long as it doesn't have a miss under full power your fine.

James

once the car goes above idle it the rpm range all the way up is smooth, it's just the idle that bugs me a bit. i'll get it taken care of at some point.

thank you,
Ryosuke

such a ricer.....

For a rotary to idle completely smooth, it has to be rich.
After about half a minute of idling rich, the ECU will lean back the idle to save fuel & reduce emmissions.
That leaner idle will normally give a few random misfires.

Of course it is, how are you going to make boost at 800rpm with a closed throttle?! An idling engine will always sit well into the vacuum side of the gauge. Making boost requires lots of airflow through the engine. Your engine is perfectly normal, stop worrying about it! ;)

It's unlikely to be timing unless someone has messed with the CAS, but it won't hurt to check. The markings on the pulley will not have rusted off, they'll just have dirt in them.

NZ, I do worry about the car as this is one of the first times I've had it running since I towed the car to my house and stripped it. it was sitting in a Barn for (what she said was) 2 years... at least. so going through everything and making sure this engine won't blow up on me is kinda high on my priorities.

thank you again. as for generating boost at idle, that was phrased wrong. I would not expect the car to be so far in vacuum at idle, more along the lines of being at or near 0mmHg.

thank you again, Oyasumi-des
Ryosuke

well.... if it was 0mm hg, that would be no vacuum. that would be more along the lines of a n/a car a wot. more vacuum at idle would actually be signs of a healthier engine, since engines are essentially just air pumps.

i suppose you can think of it as a vacuum cleaner. a healthy strong vacuum - cover the inlet - you're gonna have more vacuum. an old weak vacuum - cover the inlet - you're not gonna have much vacuum.

might not be the best way to describe it, but i'm trying. feel free to correct me if i'm wrong.

Zero is atmospheric pressure. At idle the engine is trying to suck though a very tiny opening (the closed throttle), and this creates a partial vacuum downstream of the throttle. On an NA engine the only time manifold pressure gets near zero is at WOT. It takes less than full throttle to do this on a turbo because once the throttle's part open the turbo starts to push harder.

Just watch the gauge as you drive around. You'll soon figure out how it works.

jon and NZ thank you. i'm actually starting to understand. vacuum occurs at idle, rotor passes the inlet and starts to pull air/fuel. when the throttle plates are closed however there is verry little flow to feed that suction because the throttle plates are closed, thus creating vacuum. that is why people have sucky idles if they have a vacuum leak, because the suction is being fed and reduced from elsewhere and it's strait air, not the proper mix of air and fuel. people can add a combustable (carb cleaner) to raise the air / fuel mix and try and find a vacuum leak.

am I off? thank you again

Ryosuke